HONG KONG (Reuters) – China’s Hanergy Thin Film Power Group <0566.HK> is under investigation by Hong Kong’s market watchdog, a source told Reuters just hours after the company lost half its market value of nearly $40 billion in 24 minutes on Wednesday.

Trade in the stock was suspended after the plunge, which left analysts just as puzzled about the sudden drop as they had been about a long run-up in the share price of the company, which manufactures solar panel-making equipment.

A source familiar with the situation later said Hanergy had been under investigation for several weeks by Hong Kong’s Securities and Futures Commission (SFC) for alleged market manipulation.

A spokesman for the SFC declined to comment, and Hanergy officials were not available to comment when called at their Beijing offices.

The company, controlled by founder Li Hejun, said in a statement that trade had been suspended “pending release of an announcement containing inside information”.

Before the stock plunge, Hanergy had seen its value climb five-fold since September. At its share price peak in March it was worth $48 billion, more than its nearest two dozen rivals combined and making Li one of China’s richest men – even as analysts and market watchers questioned the validity of some of its bullish proclamations.

The stock’s precipitous tumble came shortly after the beginning of the company’s annual general meeting in Hong Kong. Li did not attend the meeting, and the company’s chief executive declined to comment on the share price plunge, according to local online media reports.

Li had attended an opening ceremony for a new company centre in Beijing instead.

The 47 percent slide in the stock price left the company with a market value of $21 billion. More than 170 million Hanergy shares were traded in the first hour of Wednesday’s trading session, far more than its daily average over the past month, according to Thomson Reuters data.

Volatility on the Hong Kong Stock Exchange has increased since the creation of a link-up with Shanghai in November that has brought in massive inflows from China.

Analysts following the stock said they did not know the reason for the plunge.

“God knows. I don’t know,” said Charles Yonts, an analyst at CLSA in Hong Kong, adding that he had not noticed any change in the fundamentals of the company.

The Hong Kong Stock Exchange declined to comment on the reason for the suspension, as did the local regulator. Shares in Hong Kong can remain suspended for months.

The rout follows a 37 percent drop in the share price of U.S.-listed Chinese solar panel maker Yingli Green Energy Holding <YGE.N> overnight after it said in its annual report that there was “substantial doubt” over its ability to continue as a going concern due to indebtedness.

Yingli later said its statement had been taken out of context by some media and it was confident of its ability to service the global solar market and had taken substantive steps related to its debt repayments.

Hanergy has made bullish comments about its thin-film technology for solar panels but some experts say its products are not efficient or cheap enough to take any major market share from conventional panels made with crystalline silicons.

Another concern cited by analysts is that Hanergy relies on its parent company – Hanergy Holdings Group Ltd – for most of its revenue and profits.